During the drilling of a borehole and the lining of the borehole once drilled, tubulars, such as drill tubular and casing, must be connected into a tubular string. The tubular string is extended into a borehole by connection of joints of tubular at a drilling rig.
For example, when running or drilling with casing a top drive can be used in a drilling rig for handling the casing string. In some well operations, an engaging apparatus, including an internal or external casing gripping mechanism, can be connected below the top drive to grip a joint of casing so that the engaging apparatus and casing can be driven axially and/or rotationally by the top drive.
In a drilling rig, the top drive can be hung in the mast with the engaging apparatus connected in drive communication and in substantial axial alignment therebelow. The top drive and engaging apparatus are hung in the mast above the well center, the top drive and engaging apparatus define a main axis of the drilling rig that is aligned with well center. Joints of casing, for connection into the drill or liner string, can be supported, for example in a V-door, adjacent the main axis of the drilling rig. For connection into the drill or liner string, the casing can be engaged by an elevator and brought under the drive system for engagement and handling. Generally, the elevator is supported on link arms suspended from the top drive or the engaging apparatus or cables extending from the top drive link arms.
To pick up a casing joint, the top drive is lowered to permit the elevator, either on conventional link arms or with the cables attached to the link arms, to be moved over and engaged about a casing joint on the V-door. The top drive is then hoisted to pull the casing off the V-door. Once free of the V-door, the tubular joint can be swung by gravity under the engaging apparatus. Then the top drive is lowered so that the tubular joint can be supported in a stump of the casing string, which is supported in the rotary table. Then the gripping mechanism can engage the tubular joint and drive the casing joint into the threaded connection exposed on the stump.
In this handling, the casing thread can be damaged and the tubular dope can be lost. In addition, it is sometimes difficult to align the free end of the casing joint with the stump.